I said there would probably be more questions. :-)
We have some confusion regarding the assignment of hardware physical
addresses to the HVMs. If all 32-bit HVMs are run in legacy mode, then
they would be restricted to using 32-bit PAE shadow page tables. The
maximum physical addressing of such tables is limited to 64GB, so this
implies that all 32-bit HVMs must be located within the first 64GB of
hardware physical memory. However, your previous responses indicated
that 32-bit HVMs do not have such a restriction. So our conclusion is
that 32-bit HVMs running in legacy mode using 32-bit PAE page tables are
able to address hardware physical memory above the 64GB limit. Is this
correct? Could we create two separate 32-bit HVM guests, assign each of
them 64GB of memory, and have them run concurrently without any problems
(assuming that the platform has sufficient memory installed)?
Thanks again,
Bruce
-----Original Message-----
From: Vessey, Bruce A
Sent: Friday, December 07, 2007 1:27 PM
To: 'Mark Williamson'; xen-devel@xxxxxxxxxxxxxxxxxxx
Cc: Ian Pratt; Keir Fraser
Subject: RE: [Xen-devel] Question about implementation of 32-bit guests
on64-bit hypervisor (IDT-related)
Thanks to all of you for your answers. I think we'll have some more
questions, but we need to figure out what they are first.
- Bruce
-----Original Message-----
From: M.A. Williamson [mailto:maw48@xxxxxxxxxxxxxxxx] On Behalf Of Mark
Williamson
Sent: Friday, December 07, 2007 11:52 AM
To: xen-devel@xxxxxxxxxxxxxxxxxxx
Cc: Ian Pratt; Keir Fraser; Vessey, Bruce A
Subject: Re: [Xen-devel] Question about implementation of 32-bit guests
on64-bit hypervisor (IDT-related)
> > > guests on top of the 64-bit hypervisor?
> >
> > 32-bit PV guests are restricted to using the low 128GB of physical
> > memory.
> > There's not even that restriction for 32-bit HVM guests.
>
> We could even use shadow translate mode to get around the 128GB
> restriction, though at some performance cost. I guess you'd switch the
> guest to shadow mode if you've run out of memory below 128GB.
That's not possible right now, though, right? Shadowing PV guests was
still broken IIRC?
Cheers,
Mark
--
Dave: Just a question. What use is a unicyle with no seat? And no
pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!
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